O₂-triggered early response of lipopolysaccharide biosynthesis in Porphyromonas gingivalis

Objectives: Although P. gingivalis, by definition, cannot grow under aerobic conditions, it exhibits aerotolerance. To accomplish this, P. gingivalis must express proteins that counter oxidative stress. P. gingivalis expresses a number of potential virulence factors, including lipopolysaccharide (LPS), which may contribute to the pathogenesis of periodontitis. Our proteomic study documented that proteins involved in counter oxidative stress system such as DnaK, GroEL, and AhpC were increased by oxidative stress. The aim of this study was to examine the effect of O₂ on early response of LPS biosynthesis in P. gingivalis cells to obtain the clue to understand the mechanism resulting in this incidence. Methods: A portion of P. gingivalis late-log phase cell culture, grown either excess or limited amount of hemin, was allowed to expose air with and without pre-incubation of H₂O₂, while another portion was kept anaerobic. The extracted proteins from cultures with and without oxidative stress were separated by two-dimensional gel electrophoresis (2-DE) and stained with Pro-Q® diamond, a potent regent for detection of phosphoproteins in gel. The amount of LPS extracted was measured by colormetric manner. Results: In proteomics analysis, phosphorylation of proteins, which might be involved in LPS biosynthesis, was changed by oxidative stress. LPS production was increased by both oxidative stress and H₂O₂ incubation in cells grown under hemin limitation. Conclusion: These results suggest that LPS biosynthesis might be triggered by O₂ in P. gingivalis. Moreover, when P. gingivalis cells encounter the extracellular effecter molecules of the host's immune system, their ability to withstand and modulate the host's immune processes might be a key determinant of their long-term survival and pathogenic potential. Therefore, to clarify the effect of O₂ on LPS biosynthesis is essential to elucidate the virulence of P. gingivalis.